The objective of the proposed research is to investigate the anatomical basis for binaural hearing in insectiovores and prosimian primates. These comparative observations should (1) provide data relevant to the evolution of hearing in primates and (2) provide an anatomical basis for behavioral studies on binaural hearing and auditory localization. In the anatomical studies, modern techniques for demonstrating connectivity in the nervous system will be used to show ascending projections from the cochlear nucleus and from the superior olivary complex. It is expected that the anatomical results will provide specific hypotheses about the function of various parts of the central auditory system. Some of these hypotheses will then be tested in behavioral experiments on localization of sound in space. The capacity of experimental animals to localize sound will be tested before and after a lesion is made in the central auditory system, the locus of the lesion having been determined on the basis of the anatomical findings. A comparison of preoperative with postoperative performance will determine the effect of the lesion on localizing behavior.